The present invention relates to atomic layer deposition. More specifically, the present invention relates to an apparatus and process for improving the performance of an atomic layer deposition chamber.
A method of depositing very thin films is atomic layer deposition (ALD). This method has several advantages over tradition chemical vapor deposition. It can be performed at lower temperatures, uses a wide range of precursors, produces very thin films, inherently obtains 100% step coverage, and can be used to xe2x80x9cmicroengineerxe2x80x9d complex film matrices.
In ALD, individual precursors are pulsed onto the surface of a wafer in a sequential manner, without mixing the precursors in the gas phase. Each individual precursor reacts with the surface to form an atomic layer in a way that only one layer can form at a time. The surface reaction occurs such that the reaction is complete, and permits no more than one layer at a time to be deposited. This occurs no matter how many molecules are applied to the surface in an overdosing mode. The films are built up by introducing short bursts of gases in rapid cycles.
According to recognitions of the present inventors, two problems occur with the ALD method. One problem concerns the diversion of the flow of liquid precursors introduced in a vapor phase. During ALD processing using a liquid delivery system, it is necessary to keep an established flow of the liquid precursor in a vapor phase. In order to keep the flow active, the flow must be diverted to a fore-line of the ALD chamber when the liquid precursor is not needed in the deposition process. When the opposing gas is pulsed, the unreacted chemical is mixed in the fore-line with the diverted chemical and reacts causing a build up in the fore-line. The build up can be severe and clogs the foreline. A second problem concerns the reaction of the gases. Process gases are introduced individually for the ALD process and disposed of through the same fore lines causing the gases or vapors to react with one another.
Accordingly, there is a need for an ALD apparatus and process that minimizes clogging of the fore-line of the diverted liquid precursor. There is also a need in the art to control any area that is common to the reactive gases or vapors in a way to minimize any unwanted reaction.
These needs are met by the present invention wherein an improved ALD apparatus and process are provided. The present invention fulfills the first need of minimizing clogging of the fore-line by providing an ALD apparatus and process that allows separate chemicals to only mix when and where desired by installing and monitoring a second fore-line. The present invention fulfills the second need of minimizing the reaction of the gases in the pump lines, by allowing the reactive gases or vapors to be removed from the process reactor chamber without coming in contact with one another in an area that would create an unwanted reaction of the process gases or vapors. This is accomplished by providing independent and dedicated pumping lines and corresponding isolation valves that are activated for the specific gas when needed. The separate pump lines allow the gas to be exhausted in a manner that minimizes possible unwanted reaction of the reactive gases. Accordingly, it is an object of the present invention to provide an improved ALD apparatus and process using dispensing fore-lines and a second exhaust path in order to prevent clogging of the exhaust fore-line.